Connecting systems of the named type are disclosed, for example, in DE 101 44 039 A1 under the designation of “cone sealing coupling”. They serve for detachably connecting two hollow cylindrical pipe ends. To this end, a rotationally symmetrical connection element, which is realized in a conical and hollow manner, is connected to the first pipe end by means of friction welding once a cap nut has been placed onto the pipe end.
The side of the cone of the connection element with the smaller diameter is dimensioned such that it is able to be inserted into the oppositely-situated second pipe end. Proceeding from said side, the connection element is widened conically until beyond the diameter of the first pipe end, to which it is connected by means of friction welding. After the welding this creates a shoulder portion which serves as a support surface for holding the cap nut.
The second pipe end comprises an external thread which is realized so as to match the internal thread of the cap nut. After welding, the connection element, which is now connected in a materially-bonded manner to the first pipe end, is inserted into the second pipe end and the cap nut is screwed to the second pipe end. The screw connection presses the connection element into the second pipe end such that a sealed connection is created.
The described connection comprises several disadvantages which are shown as early as at assembly: on account of the high tightening torque of 340 Nm and of the frequently restricted installation space, special tools are necessary both at initial commissioning and replacement. Particular problems arise when flexible hoses and not solid pipes are to be connected: Torsion-free assembly is difficult as a result of difficult assembly conditions (overhead assembly, accessibility) for the required tightening torque. All in all, correct tightening of the connection is consequently not ensured in every case.
Further disadvantages are produced with regard to the causes of failure: along with the usual causes of failure of sealing cone couplings with cap nuts such as vibration, setting, relaxation and creeping, temperature-transient mechanisms in particular are responsible for failure. Up to now, this has only been countered by using a correspondingly high tightening torque and—in the case of particularly high dynamic loads and/or large temperature-transient mechanisms—cap nuts in conjunction with a lock nut. However, the safety effect of the lock nuts has not been verified in this case.
Approaches to solve these types of disadvantages are disclosed, for example, in documents DE 41 27 498 A1, FR 2 338 446, U.S. Pat. No. 925,770 and U.S. Pat. No. 2,617,672. The teaching there is to clamp the two pipe ends by means of two clamping disks, the two clamping disks acting upon a pipe end each with a clamping force and both clamping disks being screw-connected together beyond the joint of the pipe ends. The clamping force acts, in this connection, for instance, in the region of a shoulder portion at the pipe end, by means of which shoulder portion a clamping disk introduces the clamping force into the relevant pipe end.
It is, however, disadvantageous both in the case of cap nuts used up to now and in the case of the clamping disks disclosed in the prior art that the replacement of the cap nuts or of the clamping disk at the pipe end is linked with high expenditure as in the majority of cases the cap nuts or the clamping disk have to be tightened over the pipe ends in a precisely determined chronological order so that they are able to be removed from the unit or screw-connected to the unit afterwards as intended. A welding coupling, should such a one be chosen, must additionally be isolated and, after replacement of the cap nuts or clamping disk, re-welded and checked.
These types of disadvantages can be avoided to some extent by the clamping disk devices of FR 1,327,104 and U.S. Pat. No. 1,821,867, as in the case of said devices at least one clamping disk is realized as a separate circular disk ring which is detachably connected to the remaining clamping ring. Said circular disk ring can also include, for example, two separate semi-circular disk rings and is inserted into corresponding indentations in the respective pipe ends. Once the clamping disk has clamped, the clamping force is then applied from the clamping disk via the circular disk rings onto the walls of the relevant indentations in the pipe ends.
A disadvantage of said clamping disk devices, however, is the fact that the circular disk rings have to be inserted into specially provided cutouts in the pipe ends so that they are able to obtain a corresponding force transmission. In addition, the pipe ends and the clamping disks have to be machined using corresponding shaping techniques so that they are able to interact with the circular disk ring to transmit force. In addition, a precisely determined chronological order, in which individual components have to be tightened sequentially in each case over the pipe ends, has also to be adhered to in the case of said clamping disks so that they are able to be screw-connected to or detached from the pipe ends as intended.